Unsymmetrical modified leuco derivatives of indigoid dyes



Patented Nov. 15, 1938 UNITED STATES UNSYMIVIETRICAL MODIFIED LEUCO DE-RIVATIVES OF IND'IGOID DYES Arthur Lawrence Fox, Wcodstown, N. .L,assignor to E. I. du Pont de Nemours & Company, Wilmington, DeL, acorporation of Delaware No Drawing. Application October 21, 1935, SerialNo. 46,055

3 Claims.

This invention relates to new and improved indigoid dye reductionproducts and compositions, more particularly reduction products andcom,- positions of unsymmetrical indigoid dyes having dissimilarheterocylicnuclei, and a process for the preparation thereof.

The present application is a continuation-inpart of my co-pendingapplications Serial Nos. 635,198 filed September 28, 1932, and 721,413filed April 19, 1934.

It is well known that indigoid dyes may be reduced to their so-calledleuco compounds which are soluble in aqueous caustic alkalis and thatthese leuco compounds are readily converted to the original dye uponoXidation, even such as is accomplished by the action of air. This facthas been taken advantage of in the dyeing industry, wherein the indigoiddye is customarily treated with an aqueous solution containing areducing agent I and strong. caustic alkali in sufficient amount toproduce a vat containing the soluble leuco compound. The materials to bedyed are dipped in the vat so produced, and then exposed to the air,whereupon the oxygen in the air oxidizes the leuco compound to theoriginal dye. In such a process, it has always been regarded asnecessary to employ a strong caustic alkali such as sodium and potassiumhydroxides in order to produce the soluble leuco compound.

It is an object of the present invention to pro duce new and improvedmodified leuco compounds from unsymmetrical indigoid dyes havingdissimilar heterocyclic nuclei which are generally stable to air andinsoluble in water. A further object is to produce new and improved dyereduction products and compositions which are valuable in printingprocesses. A still further object is to provide a new and improvedprocess for producing products of the type above described. Otherobjects will appear hereinafter.

These objects are accomplished in accordance with my invention whichcomprises treating an unsymmetrical indigoid dye having dissimilarheterocyclic nuclei with any aqueous solution of a reducing agent suchas has been previously utilized, but in the absence of added alkali. Inother words, the reduction of the indigoid dye is carried out insubstantially the same manner as has previously been the practise,except that no alkali is added or employed other than that naturallypresent in the reducing agent. The alkali, if any, naturally present inthe reducing agent will be insuflicient as a general rule to give thesolution an alkaline reaction and in fact, when sodium hydrosulfite isemployed, the solution appears to have aslightly acid reaction.

The substances produced in accordance with this invention are generallystable towards oxidation by air. However, the stability of the variousproducts varies somewhat. Also, in some cases,

it is advantageous to acidity the products once produced, preferablyimmediately after they are formed, to render them still more stableagainst oxidation, employing a non-oxidizing acid such as hydrochloric,sulfuric, acetic, carbonic and sulfurous acids for this purpose. Thereducing agents to be employed preferably comprise sodium hydrosuliite,although other equivalent reducing agents ordinarily employed forreducing indigoid dyes, such as sodium formaldehyde sulfoxylate, may beused wholly or in part.

The temperatures at which the reduction is caused to take place may varywithin a rather Wide range but should generally be maintained aboveabout 50 C., and it willusually be found expedient to employtemperatures not above those necessary for boiling. Under atmosphericconditions, however, I have found temperature of from 70 to 100 C. to bethe preferable temperature being the most practical and efficient. Ifdesired, higher or lower temperatures may be employed.

When the reduction of an indigoid dye having dissimilar heterocyclicnuclei is accomplished in accordance with the above describedconditions, a product is formed which has a color greatly different fromthat of the original dye and which is generally insoluble in water andstable towards oxidation by the oxygen of the air. These products arevaluable in printing processes when made up into pastes.

Since the specific reactions which take place during the reductionaccomplished in accordance with my invention are not definitely knownand the chemical structure of the resulting products is also notdefinitely known, no attempt is made at the present time to give anytheoretical description of the reactions taking place or of thestructural formulas of the materials produced. In my co-pendingapplication Serial No. 46,054 filed of even date herewith, I havedescribed certain other modified leuco compounds which are also stableto air, insoluble in water andyield prints in the usual manner but withsmaller amounts of reducing agent. In general, however, the products ofsaid application do not appear to be as stable to the oxygen of the airas the products of the present application. For instance, the productsof the aforesaid application nearly always undergo what may be termed asecondary. oxidation, the freshly formed color changing almostimmediately on exposure to air to a darker color. This secondary colorchange of the freshly formed product does not usually occur with theproducts of the present invention.

, Furthermore, the shade of the stable leuco derivativeprepared inaccordance with the present application often differs pronouncedly fromthe shade of the leuco derivative prepared in accordance with theaforesaid co-pending application.

The solubility in alkalis may also differ. Thus, while the products ofthe present invention prepared in the absence of alkalis and those of myco-pending application prepared in the presence of insufficient alkalifor vatting are generally insoluble in cold, dilute (3%) sodiumhydroxide, some of the products of the present invention are soluble incold, dilute sodium hydroxide whereas the reduction products from thecorresponding dyes prepared in the presence of an alkali are insoluble.This is true in spite of the apparently greater stability of theproducts of the present invention to oxidation.

The invention will be more fully understood, but is not limited by thefollowing examples in which the quantities are stated in parts byweight. In

each example the modified leuco derivative was filtered oil, washed withdilute hydrochloric acid and color changes noted. Its color in sulfuricacid wasimmediately determined and then it was allowed to stand in openair for seventy-two hours, after which its color in sulfuric acid wasagain determined. Also, the stability of these modified leucoderivatives to cold and hot dilute alkali was examined.

Example I One part of dry 2-(52'7-dibromindol) -2-6-chlor-7-methyl-thionaphthene indigo having the formula was heated on aboiling water bath with 2 parts of sodium hydrosulfite in parts of wateruntil reduction was observed by the color change. The modified leucoderivative which precipitated was filtered, washed with dilutehydrochloric acid, and color changes noted.

The color of the original dye powder was purple, and that of the stableleuco grey changing to grey black on contact with air. The color of theoriginal dye in sulfuric acid was very blue green, and that of thefreshly prepared stable leuco green. On standing seventy-two hours incontact with air, the color of the stable leuco was dull grey lavenderwhich gave a green color in sulfuric acid. This was not affected by cold3% sodium hydroxide, but did dissolve at least in part on warming.

Example II One part of dry 2-(5'z7-dibromindol)-2-5:'I-

dimethyl-thionaphthene indigo having the for- 'mula oo 00 CH x7 Br =C 1CH3 H Br was heated on a boiling water bath with 2 parts of sodiumhydrosulfite in 50 parts of water until reduction was observed by thecolor change. The modified leuco derivative which precipitated wasfiltered, washed with dilute hydrochloric acid, and color changes noted.

The color of the original dye powder was very dark blue, and that of thestable leuco blue black changing to black on contact with air. The colorof'the original dye in sulfuric acid was very blue green; and that "ofthe freshly prepared stable leuco green. After standing seventy-twohours in air, the stable leuco was violet black in color, giving a bluegreen in sulfuric acid. The stable leuco was not affected by cold 3%sodium hydroxide, but did dissolve at least in part on warming.

Example III One part of dry 2-(5z7-dibromindol)-2'-4-methyl-thionaphthene indigo having the formula I oo oo H Br was heatedon a boiling water bath with 2 parts of sodium hydrosulfite in 50 partsof water until reduction was observed by the color change. The modifiedleuco derivative which precipitated was filtered, washed with dilutehydrochloric acid, and color changes noted.

The color of the original dye was purple, and that of the stable leucogreen, which did not change on contact with air. The color of theoriginal dye in sulfuric acid was dirty blue, and that of the freshlyprepared stable leuco brownish green. After standing seventy-two hoursin air, the stable leuco was light grey green in color and gave abrownish green in sulfuric acid. It was not affected by cold 3% sodiumhydroxide, but did dissolve at least in part on Warming.

' Example IV One part of dry 2-(5z'7-dibromindol)-2-4-methyl-bmmthionaphthene indigo having the formula washeated on a boilingwater bath with 2 parts of sodium hydrosulfite in 50 parts of wateruntil reduction was observed by the color change. The modified leucoderivative which precipitated was filtered, washed with dilutehydrochloric acid,

and color changes noted.

The color of the original dye was purple, and that of the stable leucoblue black changing to deep blue on contact with air. The color of theoriginal dye was green blue in sulfuric acid, and.

that of the freshly prepared stable leuco green. After standingseventy-two hours; the color of the stable leuco was deep lavender, andinsulfuric acid blue green. This stable leuco was not affected by cold3% sodium hydroxide, but

did dissolve at least in part on warming.

Example V One part of dry 2-(5z'7-dibromindol)-2'-4-chlor-7-methyl-thionaphthene indigo having the formula was heated on aboiling water bath with 2 parts of sodium hydrosulfite in 50 parts ofwater until reduction was observed by the color change. The

modified leuco derivative which precipitated was filtered, washed withdilute hydrochloric acid, and color changes noted.

The color of the original dye was purple, and that of the stable leucodull blue which did not change on contact with air. The original dyegave a very bright pure blue in sulfuric acid, and the freshly preparedstable leuco gave a deep green. On standing seventy-two hours in air,the stable leuco was dull blue in color, and gave a dirty green insulfuric acid. It was not affected by hot or cold 3% sodium hydroxide.

Example VI One part of dry 2-(5z7-dibromindol)-2'-5-methyl-thionaphthene indigo having the formula was heated on a boilingwater bath with 2 parts of sodium hydrosulfite in 50 parts of wateruntil reduction was observed by the color change. The modified leucoderivative which precipitated was filtered, washed with dilutehydrochloric acid, and color changes noted.

The color of the original dye was purple, and that of the stable leucodull blue, which did not change on contact with air. The original dyegave a bright pure blue in sulfuricacid, and the freshly prepared stableleuco gave an apple green color. After standing seventy-two hours incontact with air, the stable leuco was dull blue, and gave a pure greenin sulfuric acid. This stable leuco was dissolved at least in part bycold or hot 3% sodium hydroxide.

Example VII One part of dry 2-(5:7-dibromindol) -2'-'7-chlor-thionaphthene indigo having the formula co 0:0 I

01 H Br was heated on a boiling water bath with 2 parts of sodiumhydrosulfite in 50 parts of water until reduction was observed by thecolor change. The modified leuco derivative which precipitated wasfiltered, washed with dilute hydrochloric acid, and color changes noted.

The color of the original dye was purple, and that of the stable leucodull lavender, which did not change on contact with air. The originaldye gave a pure blue in sulfuric acid, while the freshly prepared stableleuco gave a blue green. On standing seventy-two hours in air, thestable leuco was violet in color and gave a blue green in sulfuric acid.It was dissolved at least in part by cold or hot 3% sodium hydroxide.

Eazample' VIII One part of dry 2-(5:7-dib-romindol)-2- 4 5 :6:7-tetramethyl-thionaphthene indigo having the formula was heated on aboiling water bath with 2 parts of sodium hydrosulfite in 50 parts ofwater until reduction was observed by the color change. The modifiedleuco derivative which precipitated was filtered, washed with dilutehydrochloric acid, and color changes noted.

The original dye was purple, and the stable leuco was grey green whichdid not change on contact with air. The original color gave a dirtygreen in sulfuric acid, and the freshly prepared stable leuco gave abrown. After standing seventy-two hours in air, the stable leuco wasdull and violet in color, and gave a brownish green in sulfuric acid. Itwas not affected by cold 3% sodium hydroxide, but did dissolve at leastin part on warming.

Example IX One part of dry 2-(5z7-dibromindol)-2-4:7-dimethyl-5-chlor-thionaphthene indigo having the formula stableleuco wasdull lavender in-color, and gave a yellow greenin sulfuric acid. It was"not affected by cold 3% sodium hydroxide, but did dissolve at least inpart on warming.

Example X One part of dry z-(5z7-dibromindol)-2-4-methyl-5-brom-7-isopropyl-thionaphthene indigo having the formula washeated on a boiling water bath with 2 parts of sodium hydrosulfite in 50parts of water until reduction was observed by the color change. Themodified leuco derivative which precipitated was filtered, washed withdilute hydrochloric acid, and color changes noted.

The color of the original dye was reddish, and that of the stable leucoblack, which did not change on contact with air. The original dye gave ablue green color in sulfuric acid, and the freshly prepared stable leucoyellow green. After standing seventy-two hours in contact with air, thestable leuco was violet black in color, and gave a blue green insulfuric acid. It was dissolved at least in part by cold or hot 3%sodium hydroxide.

Example XI One part of dry acenaphthene-4-chlor-7- methyl-thionaphtheneindigo having the formula of the stable leuco brick red, which did notchange on contact with air. The original dye gave a bright pure green insulfuric acid, and the stable leuco gave a dirty green. After standingseventy-two hours, the stable leuco was brick red in color and gave adirty green in sulfuric acid. It was not affected by cold 3% sodiumhydroxide, but was dissolved at least in part on warming.

Example XII A mixture of the following ingredients was prepared:

1 part of 2-(5z'7-dibromindol) -2-4:7-dimethylthionaphthene indigo 50parts of water 2 parts of sodium hydrosulfite These were heated togetherat the boil until reduction of the dye was observed by the color change.The modified leuco which precipitated was filtered off, washed withdilute hydrochloric acid and color changes noted.

The original color of the dye powder was violet, The modified leucocolor was reddish-brown grey, which changed to blue on short contactwith air. Its color in sulfuric acid was green, while that of theoriginal dye was blue. After standing seventy-two hours, the color ofthe modified leuco was blue and in sulfuric acid blue green. The stableleuco was very slightly affected by cold 3% sodium hydroxide anddissolved on heating the same.

Ewample XIII A mixture of the following ingredients was prepared:

200 parts of 2-(5: 7dibromindol) -2-4-methyl-6- chlorothio-naphtheneindigo 400 parts of alcohol 50 parts of sodium hydrosulfite These wereheated under reflux for two hours. At first, a brown precipitate formed,then this turned to green. After two hours, water was added and thealcohol distilled off. The product was filtered and washed. A smallportion was removed and the remainder washed with dilute hydrochloricacid.

On contact with air the product changed from green to blue. Its color insulfuric acid was pure green and remained so even after standing in openair all night.

The reaction medium is a liquid in which the stable leuco derivative isinsoluble. Thus, aqueous or alcoholic media may be used. Entirelyaqueous media or aqueous solutions of alcohol and water in which thewater preponderates will give good results. Commercial alcoholcontaining the usual proportions of water may be used satisfactorily.

The heating is effected until the formation of the air-stable leucoderivative is observed either by color change of the dye or by examininga test sample. The time may vary, for example, from fifteen minutes tofour hours.

The products of the invention which are normally prepared in an acidicmedium are practically always air-stable as soon as formed. If furtheracidification is desired, the acid may be added immediately to thereaction mixture, with or without further heating, or subsequently when.

the product has been separated.

It will be noted that the dye reduction products of Examples VI, VII andX when prepared by reduction with sodium hydrosulfite alone yieldedproducts perfectly air-stable for seventy-two hours but easily dissolvedat least in part by cold 3% sodium hydroxide.

It will be apparent that the invention is applicable to the preparationof other unsymmetrical indigoid dyes having dissimilar heterocyclicnuclei, including particularly the substituted derivatives of 2:2-thionaphthene-indolindigos, 2- thionaphthene 3 indolindigos, 2 indolacenaphthene indigos, 2 thionaphthene acenaph thene indigos, and similarunsymmetrical indigoid dyestuffs as described, for example, by Truttwin,Enzyklopadio der Kiipenfarbstoffe. Further specific examples are 2-(5:7-dibromindol) -2'- P-methyl-d-chloro)-thionaphthene indigo, 6-ethoxy-2-thionaphthene-acenaphthene indigo,bota-naphtho-quinone-2-indolindigo and4-bromo-2-alpha-naphthol-thionaphthene indigo.

The term indigoid is used generically and includes dyes which containthe grouping wherein R is an aromatic nucleus, and X represents NH, S01' Se.

In general, the preferred products of the invention are those preparedfrom dyestuffs containing non-reducible substituents such as, forexample, halogen atoms, alkyl groups and alkoxy groups in one or more oftheir aromatic nuclei. Special combinations of substituents may produceespecially desirable dye reduction products, depending upon theproperties desired. Thus, the dye reduction products of Examples III, V,VI, VII, VIII, X and XI appear to be very air stable because the freshlyprepared product undergoes no substantial color change on exposure toair. The products of Examples VI, VII and X are soluble at least in partin both cold and hot 3% caustic soda solution. The products of ExamplesIII, IV and IX are insoluble in cold 3% sodium hydroxide but are solubleat least in part in hot 3% sodium hydroxide. The process has been foundto be advantageous in the preparation of all mono-substitutedderivatives, for instance, those containing chlorine or methyl groups inthe 4-, 5-, 6- and 7- positions of the thionaphthene nucleus; also, inthe preparation of disubstituted derivatives, particularly thosecontaining a halogen atom and an alkyl group in the same nucleus.Examples have also been given of triand tetrasubstituted derivatives.The aromatic nucleus may contain more than one carbocyclic ring, as, forinstance, naphthionaphthene and naphthisatin nuclei either substitutedor unsubstituted.

The isatin nucleus may contain substituents similar to those containedin the thionaphthene nucleus.

The terms alkyl and alkoxy are used throughout the specification andclaims in their usual sense and are intended to cover such radicals asmethyl, ethyl, allyl, isopropyl, butyl, methoxy, ethoxy, butyloxy andthe higher alkyl and alkoxy radicals.

Dye compositions may be prepared by mixing the stable leuco derivativein dry or paste form with auxiliary agents such as metal compounds, forinstance, the oxides and salts of iron, and agents such as diethyleneglycol. Especially desirable results have been obtained in printing dyecompositions containing the stable leuco derivative together with bothdiethylene glycol and an iron salt. Dispersing agents such as, forexample, alkali metal salts of the condensation product of formaldehydewith sulfonated naphthalene may be included in the dye composition.

In the preparation of printing pastes, the usual auxiliary agents suchas alkalis, e. g., sodium hydroxide, sodium carbonate and/or potassiumcarbonate, reducing agents as, for instance, sodium formaldehydesulfoxylate, glucose or preservers syrup, hygroscopic agents such asglycerin, and thickeners may be employed.

A representative printing paste may be prepared by mixing the followingingredients:

'20. 0 parts of an 8% suspension of the modified leuco body 9. 1 partsof potash 6. 6 parts of sodium formaldehyde sulfoxylate 10. 0 parts ofglycerin 54. 3 parts of thickener The thickener employed is prepared bymixing:

1 part of Wheat starch 3 parts of British gum 4 parts of water 1 part ofgum trag-acanth (6% solution) This mixture is boiled for ten to fifteenminutes and then cooled, whereupon it is ready for incorporation in thepaste.

The paste prepared as above is printed on the desired material, allowedto dry and aged for about five minutes at about 214-216 F. The materialis then subjected to oxidation, rinsed, soaped, rinsed again, and thendried.

Preferred dye compositions are those containing at least 0.5% diethyleneglycol, based on the weight of the dye, and about 0.1 to about 5.0% of ametal salt such as an iron salt. Smaller or larger proportions of theseingredients may be used; for instance, the amount of diethylene glycolmay be as much as four times the weight of the dye paste. A typicalprinting paste containing diethylene glycol instead of glycerin has thefollowing composition:

20 parts of the stable reduction product (12.5%

paste) 1'? parts of potash 12 parts of sodium formaldehyde sulfoxylate 3parts of diethylene glycol 48 parts of thickener If desired, one-half orone-third as much sodium formaldehyde sulfoxylate may be employed withthe corresponding increase in the amount of thickener. The stable leucobodies have also been printed without any reducing agent, for

instance, by the use of the following representative printing paste:

Improved results are obtained by the addition of 1% of FeClzA=H2O to anyof the above identified dye compositions.

The invention is especially advantageous in providing new and improveddyestuffs and dye compositions. These new and improved dye reductionproducts and dye compositions are particularly useful in printing andmake possible the production of stronger and brighter prints thanheretofore obtainable from the dyestuif proper. Furthermore, they may beprinted with smaller amounts of reducing agent, which is an advantage tothe consumer.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that I do not limit myself to the specific embodimentsthereof except as defined in ,the appended claims.

I claim:

1. The process of preparing reduction products of thionaphtheneindolindigoid dyes which comprises reducing a thionaphtheneindolindigoid dye which is mono-substituted in the aromatic portion ofthe thionaphthene nucleus by a substituent selected from the groupconsisting of halogen, lower alkyl and lower alkoxy radicals, with analkali metal hydrosulfite reducing agent in an aqueous medium in theabsence of added alkalies and which is acidic during the reduction.

2. The process of preparing reduction products of thionaphtheneindolindigoid dyes which comprises reducing a thionaphtheneindolindigoid dye di-substituted by two different substituents selectedfrom the group consisting of halogen, lower alkyl and lower alkoxyradicals, with an alkaline metal hydrosulfite reducing agent in anaqueous medium in the absence of added alkalies and which is acidicduring reduction.

3. The process of preparing stable reduction products of unsymmetricalthionaphthene-indole-indigoid dyes which comprises reducing anunsymmetrical thionaphthene indole-indigoid dye having dissimilarheterocyclic nuclei solely with an alkali metal hydrosulfite reducingagent in aqueous medium until a change of color is brought about and astable reduction product is produced, but not until the dye istransformed to a soluble form, and then separating the product.

ARTHUR L. FOX.

